Recently, a secondary battery, which can be charged and discharged, has been widely used as an energy source for wireless mobile devices. Also, the secondary battery has attracted considerable attention as a power source for electric vehicles (EV) and hybrid electric vehicles (HEV), which have been developed to solve problems, such as air pollution, caused by existing gasoline and diesel vehicles using fossil fuel.
Small-sized mobile devices use one or several small-sized cells for each device. On the other hand, medium- or large-sized devices, such as vehicles, use a medium- or large-sized battery module having a plurality of battery cells electrically connected with each other because high output and large capacity are necessary for the medium- or large-sized devices.
Preferably, the medium- or large-sized battery module is manufactured with small size and small weight if possible. For this reason, a prismatic battery or a pouch-shaped battery, which can be stacked with high integration and has a small weight to capacity ratio, is usually used as a battery cell of the medium- or large-sized battery module. Especially, much interest is currently generated in the pouch-shaped battery, which uses an aluminum laminate sheet as a sheathing member, because the pouch-shaped battery is lightweight and can be manufactured with low costs.
FIG. 1 is a perspective view typically illustrating a conventional representative pouch-shaped battery. The pouch-shaped battery 10 shown in FIG. 1 is constructed in a structure in which two electrode leads 11 and 12 protrude from the upper end and the lower end of a battery body 13, respectively, while the electrode leads 11 and 12 are opposite to each other. A sheathing member 14 comprises upper and lower sheathing parts. That is, the sheathing member 14 is a two-unit member. An electrode assembly (not shown) is received in a receiving part, which is defined between the upper and lower sheathing parts of the sheathing member 14. Opposite sides 14a and upper and lower ends 14b and 14c, which are contact regions of the upper and lower sheathing parts of the sheathing member 14, are bonded to each other, whereby the pouch-shaped battery 10 is manufactured. The sheathing member 14 is constructed in a laminate structure of a resin layer/a metal film layer/a resin layer. Consequently, it is possible to bond the opposite sides 14a and upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14, which are in contact with each other, to each other by applying heat and pressure to the opposite sides 14a and upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 so as to weld the resin layers to each other. According to circumstances, the opposite sides 14a and upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 may be bonded to each other using a bonding agent. For the opposite sides 14a of the sheathing member 14, the same resin layers of the upper and lower sheathing parts of the sheathing member 14 are in direct contact with each other, whereby uniform sealing at the opposite sides 14a of the sheathing member 14 is accomplished by welding. For the upper and lower ends 14b and 14c of the sheathing member 14, on the other hand, the electrode leads 11 and 12 protrude from the upper and lower ends 14b and 14c of the sheathing member 14. For this reason, the upper and lower ends 14b and 14c of the upper and lower sheathing parts of the sheathing member 14 are thermally welded to each other, while a film-shaped sealing member 16 is interposed between the electrode leads 11 and 12 and the sheathing member 14, in consideration of the thickness of the electrode leads 11 and 12 and the difference in material between the electrode leads 11 and 12 and the sheathing member 14, so as to increase sealability.
However, the mechanical strength of the sheathing member 14 is low. In order to solve this problem, there has been proposed a method of mounting battery cells (unit cells) in a pack case, such as a cartridge, so as to manufacture a battery module having a stable structure. Also, a device or a vehicle, in which a medium- or large-sized battery module is installed, has a limited installation space. Consequently, when the size of the battery module is increased due to the use of the pack case, such as the cartridge, the spatial utilization is lowered. Due to the above-mentioned low mechanical strength, the battery cells repeatedly expand and contract during the charge and the discharge of the battery cells. As a result, the thermally welded regions may be easily separated from each other.
Since the battery module is a structure including a plurality of unit cells, which are combined, the safety and the operating efficiency of the battery module are lowered when overvoltage, overcurrent, and overheat occurs in some of the unit cells. Consequently, means for detecting the overvoltage, the overcurrent, and the overheat are needed. Specifically, voltage and temperature sensors are connected to the battery cells so as to detect and control the operation of the battery cells in real time or at predetermined time intervals. However, the attachment or the connection of the detecting means complicates the assembly process of the battery module. In addition, short circuits may occur due to the provision of a plurality of wires.